1277. 统计全为 1 的正方形子矩阵

class Solution {
    public int countSquares(int[][] matrix) {
        if(matrix.length == 0 || matrix[0].length == 0) return 0;
        int m = matrix.length, n = matrix[0].length;
        int[][] dp = new int[m][n]; // dp[i][j]表示以（i，j）为右下角的最大正方形边长
        int res = 0;
        for(int i = 0; i < m; i++) {
            dp[i][0] = matrix[i][0];
            res += dp[i][0];
        }
        for(int i = 1; i < n; i++) {
            dp[0][i] = matrix[0][i];
            res += dp[0][i];
        }
        for(int i = 1; i < m; i++) {
            for(int j = 1; j < n; j++) {
                if(matrix[i][j] == 1) dp[i][j] = Math.min(dp[i-1][j],Math.min(dp[i][j-1],dp[i-1][j-1])) + 1;
                res += dp[i][j];
            }
        }
        return res;
    }
}